Vinyl siding panels are widely used for protecting the exterior walls of buildings, as well as for enhancing the exterior appearance of buildings. The siding panels may have different profiles and exterior finishes, to provide variety in the exterior appearance they can provide to a building. Typically, the siding panels are nailed or otherwise secured to the building to fix them in place.
Formerly, in constructing vinyl siding panels, it was customary to extrude a sheet of vinyl with the entire profile formed therein, and to then cut the sheet of vinyl into panels of appropriate lengths. The sheet utilized conventional color concentrators designed to give it a desired coloration properties. The sheets could also be embossed or otherwise formed to add ornamentation to more closely simulate natural wood siding products.
In recent years the vinyl siding industry has switched to “post formed” vinyl siding, in which the siding is extruded as a flat sheet and then formed into the desired shape in post forming operations.
The industry has also switched from solid vinyl siding panels to co-extruded panels having a base substrate and an outer layer (commonly called a “capcoat” or “capstock” layer. The substrate layer is hidden from view when the siding is applied to a building, and is typically formed of conventional, relatively inexpensive but sturdy polyvinyl chloride (also known as rigid PVC). The substrate typically utilizes conventional color concentrators designed to give it a desired coloration properties. The outer layer forms the exposed, outer component of the vinyl product. The known capstock typically is formed of the same composition as the substrate (including the color concentrators), and often includes a material that forms accent color streaks in the formed capstock layer. This is described in U.S. Pat. Nos. 5,387,381, 5,866,054, 5,866,639, and 5,869,176 which are incorporated herein by reference in their entirety. The methods and products described in the these patents can produce variegated siding panels having a natural, wood grain-like appearance, but which do not provide for adequate weathering properties nor an adequate depth of color. Specifically, these teach a capstock that includes a background color and accent color streaks, and the substrate therefore does not significantly contribute to the apparent color of the panel, so as to limit the depth and appearance of the color.
PVC siding panels typically include titanium dioxide as an UV inhibitor. Titanium dioxide has a dual function in polyvinyl chloride articles such as variegated vinyl siding. Titanium dioxide stabilizes the polyvinyl chloride used in the substrate and capstock against the adverse effects of ultraviolet (“U.V.”) radiation by absorbing, reflecting, dispersing or scattering the incident U.V. energy, and also provides a white coloration of the panel since titanium dioxide is a white pigment which makes the material at least opaque and prevents it from being translucent. Titanium dioxide is the brightest white pigment with the highest opacity of any commercial product.
Unfortunately, the amount of titanium dioxide necessary for effective U.V. stabilization, about 3 parts per hundred parts of base polymeric material, precludes dark coloration of the variegated vinyl articles. Typically, only colored articles of pastel shades can be obtained; deep shades of brown, blue and maroon, for example, are not readily attainable.
Another problem that commonly occurs in variegated vinyl sidings is edge visibility. When observing a variegated siding panel from its side (i.e. along the edge of the panel), coloration differences between the capcoat layer and underlying substrate are readily apparent. These coloration differences are mainly due to the presence of the accent color streaks within the capcoat layer. Substantial costs, in terms of scrap (either during the startup or changeover of lines) may accrue in determining the proper formulation of capcoat tinting that is needed in order to match the capcoat color to the underlying substrate when observing the variegated panel along an edge.
It is thus highly desirable to produce a U.V. stable variegated siding panel that is capable of achieving dark (or “deep”) coloration. It is also highly desirable to reduce or eliminate the need for capcoat tinting to eliminate edge visibility problems. It is also desirable that such a panel be produced using conventional extrusion line equipment.